fix(street-level): review round — safer docking, mount retry, provider fallthrough

- Only a user's own collapse docks a floating window; cockpit entry,
  restores and the Cyber accordion no longer dock it or delete its saved
  place, and the accordion leaves floating windows alone.
- The viewer host records an adapter as active only after its mount
  succeeds, so a library that failed to load once is retried; concurrent
  opens share one mount, and unmounting mid-mount leaves nothing active.
- openNearest tries every active provider; one provider's error (no key,
  offline) no longer hides the others' imagery.
- The SINCE readout shows its cut-off date as soon as the committed value
  matches the thumb, even while the slider keeps focus.
- A floating window that was only dragged is bounded to the viewport and
  scrolls instead of running off-screen.
- getStats summarises coverage (summarizeCoverage) instead of building a
  full UI snapshot every second; disable() uses credits.hideAll(); smaller
  cleanups in the viewer host and sequence snapshot.
- Unit tests: panel docking and header double press, viewer-host mount
  retry/sharing/cancel, coverage summary.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/layers/streetLevel/viewerHost.test.mjs

@@ -0,0 +1,89 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { createViewerHost } from './viewerHost.js';
+
+function harness(adapter) {
+  const state = {
+    enabled: true,
+    notify() {},
+    providers: new Map(),
+    street: { host: {}, renderMode: 'letterbox', follow: false },
+  };
+  const def = { id: 'mapillary', name: 'Mapillary', label: 'MAPILLARY' };
+  state.providers.set('mapillary', { def, instance: { viewer: adapter } });
+  const parts = {
+    marker: { set() {}, clear() {} },
+    follow: { followCamera() {}, lookAtPosition() {} },
+  };
+  return { state, host: createViewerHost({ state, parts }) };
+}
+
+function fakeAdapter({ failMounts = 0 } = {}) {
+  const calls = { mount: 0, open: [], unmount: 0, listeners: 0 };
+  let emit = null;
+  return {
+    calls,
+    async mount() {
+      calls.mount++;
+      if (calls.mount <= failMounts) throw new Error('library failed to load');
+    },
+    async open(id) {
+      calls.open.push(id);
+      emit?.({
+        providerId: 'mapillary',
+        imageId: id,
+        position: { lon: 1, lat: 2 },
+        bearing: 90,
+        isPano: false,
+        externalUrl: `https://example.test/${id}`,
+      });
+    },
+    close() {},
+    unmount() {
+      calls.unmount++;
+    },
+    resize() {},
+    onPose(listener) {
+      calls.listeners++;
+      emit = listener;
+      return () => {
+        calls.listeners--;
+        emit = null;
+      };
+    },
+  };
+}
+
+test('a failed mount is retried on the next open instead of being cached', async () => {
+  const adapter = fakeAdapter({ failMounts: 1 });
+  const { state, host } = harness(adapter);
+  await host.open('mapillary', 'a');
+  assert.equal(state.street.error, 'library failed to load');
+  assert.equal(adapter.calls.listeners, 0, 'the pose listener was released');
+  await host.open('mapillary', 'b');
+  assert.equal(state.street.error, null);
+  assert.equal(adapter.calls.mount, 2);
+  assert.deepEqual(adapter.calls.open, ['b']);
+  assert.equal(state.street.imageId, 'b');
+  assert.equal(state.street.externalUrl, 'https://example.test/b');
+});
+
+test('concurrent opens share one mount and one pose listener', async () => {
+  const adapter = fakeAdapter();
+  const { host } = harness(adapter);
+  await Promise.all([host.open('mapillary', 'a'), host.open('mapillary', 'b')]);
+  assert.equal(adapter.calls.mount, 1);
+  assert.equal(adapter.calls.listeners, 1);
+});
+
+test('unmounting while a mount is in flight does not leave it active', async () => {
+  const adapter = fakeAdapter();
+  const { state, host } = harness(adapter);
+  const opening = host.open('mapillary', 'a');
+  host.unmount();
+  await opening;
+  assert.equal(host.activeProviderId(), null);
+  assert.equal(adapter.calls.listeners, 0);
+  assert.equal(adapter.calls.unmount, 1);
+  assert.equal(state.street.open, false);
+});